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Eye-squint-cheek-bulge means 'ouch'

THE facial expressions of mice can be used to assess the amount of pain they are in. Such discoveries could help animal workers such as vets detect physical discomfort in animals more reliably.

To identify the facial tics that indicate pain, Jeffrey Mogil of McGill University in Montreal, Canada and colleagues filmed mice for 30 pain-free minutes and then for 30 more after inducing mild pain.

They used this footage to draw up a “mouse grimace scale” based on changes in the face such as squinting eyes and bulging cheeks.